Removal of impurities from hydrocarbon oxidation products



United States Patent REMOVAL OF IMPURITIES FROM HYDRO- CARBON OXIDATION PRODUCTS William H. Clingman, In, Texas City, Tex., assignor to The American Oil Company, Texas City, Tex., a corporation of Texas No Drawing. Application June 5, 1956 Serial No. 589,370

4 Claims. (Cl. 260-533) ylic acids, organic nitrogen compounds are produced as by-products. For example when cyclohexane is oxidized to adipic acid, using nitric acid or nitrogen dioxide, the liquid portion of the oxidation products contains a small amount of undesirable nitro compounds which are exceedingly difficult to remove. These nitro compounds consist of nitrites, nitro derivatives etc. of the hydrocarbons oxidized. Unless these impurities are removed from the adipic acid, they interfere with the subsequent use of adipic acid in manufacturing good quality ultimate products such as nylon etc.

An object of this invention is to provide a process for removing the organic nitrogen compound impurities from the hydrocarbon oxidation products obtained when using nitric acid or nitrogen dioxide as the oxidizing means. Another object is to provide a process which enables the recovery of a high percentage of the carboxylic acids produced while still maintaining a high degree of organic nitrogen compound removal therefrom. Other objects and advantages of the invention will be apparent from the more detailed description thereof.

It has been found that the organic nitrogen compound impurities, which are formed during the oxidation of hydrocarbons to carboxylic acids in the presence of nitric oxide or nitrogen dioxide, can be removed from the carboxylic acids formed by neutralizing an aqueous solution of the oxidation products containing the carboxylic acids so that it has a pH of at least 7, but preferably at least 8 and not more than 10, and then contacting the aqueous solution with an activated carbon. The organic nitrogen compound impurities are adsorbed upon the activated carbon, the carboxylic acids remaining as salts in the aqueous solution. Thereafter the activated carbon is separated from the aqueous solution and the carboxylic acids recovered from the aqueous solution by procedures well-known in the art.

Although the process of this invention is applicable to the removal of organic nitrogen compound impurities contained in the oxidation products produced by oxidizing aliphatic hydrocarbons such as olefins and parafiins having from 2 to 20 carbon atoms to carboxylic acids using nitric acid or nitrogen dioxide with or without free oxygen, it will be described principally with reference to the removal of such impurities from the products obtained by oxidizing naphthenes to dicarboxylic acids. The oxidation of naphthenes such as cycloalkanes having 5 or 6 carbon atoms in the ring and their methyl-, ethyl-, propyl-, or butyl-substitutiou products to produce adipic acid (and also succinic and glutaric acids) and its alkyl substitution products by the use of N0 as the oxidizing means is known. The use of nitric acid in the oxidation of naphthenes is also a widely known process. Detailed aqueous solution.

descriptions for carrying out the oxidation process are available in the prior art.

After the oxidation reaction has been completed, the gaseous products are separated from the normally liquid oxidation products. The liquid oxidation products gen erally consist of two phases, a supernatant layer of unreacted hydrocarbons and an aqueous layer containing carboxylic acids contaminated with the organic nitrogen compound impurities. To insure full recovery of the carboxylic acids, the separated hydrocarbon layer is washed with water to dissolve the carboxylic acids, and the washings are then added to the aqueous layer of oxidation products. The general practice customarily followed in recovering the adipic acid from the aqueous solution consists of cooling the aqueous solution to a temperature at which the adipic acid crystallizes therefrom. The crystals of adipic acid, however, are contaminated with the organic nitrogen compound impurities. In the process of this invention, the organic nitrogen compound impurities are removed from the aqueous solution before recovering the adipic acid and/ or other carboxylic acids from the If desired, the invention may be practiced on the crystallization mother liquors or at any other stage in the recovery of the acids from the aqueous solution of oxidation products.

The organic nitrogen compound impurities cannot bev removed by the use of solvents such as ether, chloroform etc. because the solvents extract the carboxylic acids as well as the nitrogen compound impurities. Because of their very low volatility, the organic nitrogen compounds cannot be separated by vacuum distillation. The separation cannot be effected by forming insoluble salts of the carboxylic acids since the nitrogen compounds are adsorbed on these salts. I have found, however, that the organic nitrogen compounds can be removed from the aqueous solution of carboxylic acids by adsorbing them upon an activated carbon in a neutral solution. If the aqueous solution of the liquid oxidation products has a pH of less than 7, the activated carbon will adsorb the adipic acid as well as the organic nitrogen compounds and only a minor amount of adipic acid will be recovered from the attempted purification. If the pH of the aqueous solution is at least 7, the organic nitrogen compounds are adsorbed upon the activated carbon but the adipic acid is adsorbed to only a small extent. Thus a pH of 7 to about 14 can be used. The amount of adsorption of adipic acid upon the activated carbon can be minimized by using a pH of at least 8 but not more than about 10. This enables maximum recovery of high purity adipic acid.

In neutralizing the aqueous solution of the liquid oxidation products, a basic reagent, preferably an alkali metal containing basic reagent, is employed. For example, the alkali metal hydroxides, oxides, carbonates; the alkaline earth metal oxides, hydroxides, carbonates, sulfides etc. are highly useful for this purpose, although obviously many other basic reagents such as ammonium hydroxide, organic amines such as alkanol amines, etc. can be used. It is preferred to carry out the neutralization prior to contacting the aqueous solution with the activated carbon since this enables greater recoveries of adipic acid i. e. lesser amounts of adipic acid are adsorbed upon the activated carbon.

The aqueous solution of the liquid oxidation products which contains the adipic acid and organic nitrogen compound impurities may be contacted With the activated carbon in a batch contacting process or in a continuous process wherein the aqueous solution is slowly percolated through the layer of activated carbon. A multi-stage process or counter current operation may be used. The contacting is carried out for a period of time sufficient to adsorb the nitrogen compounds e. g. 1 minute to 2 hours. It may be carried out at temperatures of from 20to 50 C, although higher or lower temperatures may of course be used, dependingfin part upon the boiling point of the. carboxylic acidtobelrecoyered. a

The activated carbon which is..use d;.is a. -high surfacei material which is commonly known as. activated carbon 7 or. activated charcoal- The total surface area ofsuch activated carbons generally ranges between 2x105 and" 6X10 sq. cm. per gm. It .islgenerally'prepared bycarbonizingwood, peat,cellulose waste, bones, coconut shells, corn cobs. or the like to producea carbon which is then crushed to the desired size, following which the crushed material is activated by heating to an'elveatedltemperature in an. atmosphere of. steam, carbon dioxide etc. until. the desired activity has beenattained. .An activatedcharcoal. prepared from coconut shells is highlysatisfactory. Theactivated carbon is contacted with theaqueoussolu'; tion of liquid oxidation products. containing. carboxylic acid and organic nitrogen compound impurities'in an amount sufficient to adsorb, the nitrogen compounds. CQllr. tained therein. Thus the amount employed, based upon the amount of aqueous solution, depends uponthe con.- centration of the organic nitrogen'compounds. Usually one kilogram ofthe activated carbon will adsorb from 2 to 3 gms. of the organic nitrogen compound impurities. Complete adsorption'of these impurities is indicated by a change in color of the aqueous solution from yellow (the yellow color being caused by the organic nitrogen compound impurities) to water white. The activated a carbon which has become saturated with the organicni trogencompounds can be partly regeneratedbytreatment with a caustic solution such as 1 N NaOH. After the organic nitrogen compound impurities have been ad sorbed from the neutralized aqueous solution of the oxidation products, the adipic acid can be recovered by-well-. known procedures. For instance,.the neutralized solution may be acidified to release theadipic acid. followed by distillation orcrystallization to; recover the adipic acid.

Certain laboratory: experiments were. carried out relative to the purification of adipic acid solutions contaminated with organic nitrogen compound impurities. In a 4. experiments the charcoal treated solution was evaporated to reduce its volume and the adipic acid precipitated by adding HCl. The adipic acid obtained in this manner was dried at 110 C. without recrystallization, and its melting point determined. A one degree lowering of the melting point correspondsitoga; purity of about 98.4- 99.0%., A utwo degree lowering of the melting point corresponds. to apurity. of 96.7 98,.0.%. The absence of the organic nitrogen compounds from the charcoal treatsolutions. Thetoriginal untreated solutions wereyellow ed solutions was show r y' h s meltingipo nts udie he fact. that" the characteristic red andyellowsaltsof: the organic nitrogen compounds were not detectedL-inthe basic in color while the can; ot i thecharcoal treated solutions was water white. The effectiveness of the treatment with charcoalat'various .pHs-usingl-methods A and B is shown in Table I which follows:

Admin acid recovered using Method B.

.pHca'. 14.1 a V It is evident from the above table that the purified adipic acidhasapurity of approximately 99 mol percent. Itisl also apparent that the pH at which the charcoal treatment; is carried out is critically importantin its effect upon-the amount'of adipic acid recovered, i. a, it be. at least 7 and is preferably between about 8 and l0.

typical experiment 208.] gms. of an aqueous solution containing 1.09 gms. of adipic acid per 100 gms. of solution were placed in a beaker, Organic nitrogen compound im-w purities obtained from the oxidation of tertiarybutylc'yclo:

- hexane with HNO and O (120 p. s. i. g.) at 90:95 C}.

inthepresence ofH SO were used in certain experiments and the organic nitrogen compound impurities obtained, by the N0 oxidation of tertiarybutylcyclohexane:Were used. in others. The organic nitrogen compound impurities were added inv the amount of 0.04 gms. toi the'208i1' gms. of solution. The adipic acid used was commercial adipic acid having a M. P. of l54.155 C. Two procedures were employed in'the purification experiments. In method A the aqueous solution of adipic acid and organic nitrogen compound impurities was neutralized by adding thereto. an amount of 2 N KOH or NaOH solution until the. proper pH was reached and the activated carbon added thereafter. In method B the activated carbon was added to the aqueous solution of adipic acid and organic nitrogen compounds prior to neutralizing the aqueous solution. The activated carbon employed was 49.8 gms. of 50 min. 6-14 mesh activated charcoal. The mixture was stirred at about 30 C. for about one hour. Thereafter. the charcoal was filtered off and washed three times with distilled water.

The amount of adipic acid in the treated-solution'was determined by'precipitating its insoluble silver salt, dis solving the salt in 1 N HNO and determining the silver' in the solution by titration with NaCl. In certain of the It will also be noted that method A, wherein the: adipic acidsolution is neutralized. before adding the activated charcoal, enables a greater recovery of adipic acidthan does method B wherein theiadipic, acid solufionis neutralized after the activated charcoal'has' been added. Thus having described the invention what is claimed is: 1. A process for removing organic nitrogen compound im ur t es, f e he orm l liquid da on Pr ducts p q' s df by oxid z n n e hene hydrocarbons to b hoxylic acids using an. oxidizing agent'selected from the smi e o iti e mp und i ti f n c a id, and nitrogen dioxide which removal process comprises contacting. a neutralized aqueous solution of the nor mally, liquid oxidation products having a pH. of at least I with. an activated arbon wher by he O i nit ogen c mpo nd. mpnri iesare removed from the solution :of normally liquid'oxidation products by adsorption on said carbon/a d epa at he solution of o ma iqui oxidation. products from, the activated, carbon containmig adsorbed organic nitrogen compound impurities.

2..- The PIQ$ o l im where n he quequ l so ut of th norma ly iqu x d Prod ts? eu a ed 3.- PIQ$$ f l iml Wh minth s as 'fl u e -na ha 10- The w ni 1 rei t e oxidizing a en Jt a j st ne.

t stat men m Q s i a e Sai new 

1. A PROCESS FOR REMOVING ORGANIC NITROGEN COMPOUND IMPURITIES FROM THE NORMALLY LIQUID OXIDATION PRODUCTS PRODUCED BY OXIDIZING NAPHTHENE HYDROCARBONS TO CARBOXYLIC ACIDS USING AN OXIDIZING AGENT SELECTED FROM THE GROUP OF NITROGEN COMPOUNDS CONSISTING OF NITRIC ACID AND NITROGEN DIOXIDE WHICH REMOVAL PROCESS COMPRISES CONTACTING A NEUTRALIZED AQUEOUS SOLUTION OF THE NORMALLY LIQUID OXIDATION PRODUCTS HAVING A PH OF AT LEAST 7 WITH AN ACTIVATED CARBON WHEREBY THE ORGANIC NITROGEN COMPOUND IMPURITIES ARE REMOVED FROM THE SOLUTION OF NORMALLY LIQUID OXIDATION PRODUCTS BY ADSORPTION ON SAID CARBON, AND SEPARATING THE SOLUTION OF NORMALLY LIQUID OXIDATION PRODUCTS FROM THE ACTIVATED CARBON CONTAINING ADSORBED ORGANIC NITROGEN COMPOUND IMPURITIES. 